1. Field of the Invention
This invention relates to a process for preparing hexamethylphosphoramide.
2. Description of the Prior Art
Hexamethylphosphoramide is a well known compound having a variety of utilities, for example, as a solvent in polyacrylonitrile spinning operations and in processes for removing acetylene from gas streams. It is commonly prepared by reacting phosphorus oxychloride and an excess of dimethylamine in an inert organic solvent. Upon completion of the reaction the by-product dimethylamine hydrochloride is filtered off and the hexamethylphosphoramide, dimethylamine and organic solvent are separated by distillation. Inert organic solvents which are useful in such a reaction include chloroform, ethers, such as dipropyl ether and dibutyl ether, and aromatic and substituted aromatic compounds, such as benzene, ethyl benzene and xylene. Such prior art processes may provide difficulties due to the poor filterability of the by-product dimethylamine hydrochloride. Moreover, since the hexamethylphosphoramide is soluble in the organic solvent, isolation of the desired product requires separation thereof from the solvent. Representative prior art processes for the preparation of hexamethylphosphoramide are included in U.S. Pat. Nos. 2,662,095 and 3,084,190.